This invention relates to refrigeration apparatus. In particular, it relates to apparatus for depositing solid carbon dioxide on items to be refrigerated.
It is desirable to store perishable foodstuffs and other items in a chilled environment prior to their human consumption. In for example handling pre-packed meals before they are loaded onto an aircraft, the meals are taken out of a refrigerated chamber and placed in an unrefrigerated cart on the ground ready for loading onto the aircraft. On occasions, particularly if there are delays to the aircraft taking off, this procedure may result in the meals being held outside a refrigerated environment for too long a period of time to be acceptable.
It is well known that if a stream of liquid carbon dioxide at a pressure and temperature above its triple point is caused to undergo a reduction in pressure, to below the triple point pressure, the stream of liquid carbon dioxide is convened to a mixture of gas and solid carbon dioxide particles, the latter often being referred to carbon dioxide snow. Accordingly, a simple device, often referred to as a "snow horn", including a nozzle for reducing the pressure of a liquid carbon dioxide stream such that it is convened into solid carbon dioxide and gaseous carbon dioxide, and a chamber in communication with the nozzle and having an open downstream end may be used to project solid carbon dioxide at items to be refrigerated. Such a snow horn has been used to project solid carbon dioxide onto pre-packaged meals before these meals are loaded onto an aircraft in order to provide refrigeration for these meals. The practice has been for the meals to be loaded onto the shelves of a cart having doors at either end and then for a hand-held snow horn to be used to spray solid carbon dioxide particles onto the packages through one pair of doors and then through the other. It is however difficult to obtain a relatively uniform distribution of the solid carbon dioxide snow by such a method. The invention aims at providing an apparatus that ameliorates this difficulty.